JP H05(1993)-290844 A, for example, discloses that, in a lithium secondary battery using a LiPF6-containing electrolyte solution, a mixture of natural graphite and artificial graphite is used as a negative electrode material capable of absorbing and releasing lithium. The publication discloses that the mixture contains 10 weight % to 50 weight % of artificial graphite. The publication also discloses that such a configuration can inhibit the LiPF6 and the carbon material from undergoing violent reactions.
JP 2009-64574 A discloses a lithium-ion secondary battery comprising a plurality of negative electrode active material layers formed on a negative electrode current collector, in which a negative electrode active material layer more distant from the negative electrode current collector shows higher charge rate performance than a negative electrode active material layer closer to the negative electrode current collector.